1. Field of the Invention
This invention relates to oxo-imidazopyridine-carboxamides that bind with high selectively and high affinity to the benzodiazepine site of GABAA receptors. This invention also relates to pharmaceutical compositions comprising such compounds and to the use of such compounds in treatment of central nervous system (CNS) diseases.
2. Description of the Related Art
The GABAA receptor super-family represents one of the classes of receptors through which the major inhibitory neurotransmitter, xcex3-aminobutyric acid, or GABA, acts. Widely, although unequally, distributed through the mammalian brain, GABA mediates many of its actions through a complex of proteins called the GABAA receptor, which causes alteration in chloride conductance and membrane polarization. In addition to being the site of neurotransmitter action, a number of drugs including the anxiolytic and sedating benzodiazepines bind to this receptor. The GABAA receptor comprises a chloride channel that generally, but not invariably, opens in response to GABA, allowing chloride to enter the cell. This, in turn, effects a slowing of neuronal activity through hyper-polarization of the cell membrane potential.
GABAA receptors are composed of five protein subunits. A number of cDNAs for these GABAA receptor subunits have been cloned and their primary structures determined. While these subunits share a basic motif of 4 membrane-spanning helices, there is sufficient sequence diversity to classify them into several groups. To date at least 6xcex1, 3xcex2, 3xcex3, 1xcex5, 1xcex4 and 2xcfx81 subunits have been identified. Native GABAA receptors are typically composed of 2xcex1, 2xcex2, and 1xcex3 subunits (Pritchett and Seeburg Science 1989; 245:1389-1392, and Knight et. al., Recept. Channels 1998; 6:1-18). Various lines of evidence (such as message distribution, genome localization and biochemical study results) suggest that the major naturally occurring receptor combinations are xcex11xcex22xcex32, xcex12xcex23xcex32, xcex13xcex23xcex32, and xcex15xcex23xcex32 (Mohler et al. Neuroch. Res. 1995; 20(5):631-36).
The GABAA receptor binding sites for GABA (2 per receptor complex) are formed by amino acids from the xcex1 and xcex2 subunits. Amino acids from the xcex1 and xcex3 subunits together form 1 benzodiazepine site per receptor. Benzodiazepines exert their pharmacological actions by interacting with the benzodiazepine binding sites associated with the GABAA receptor. In addition to the benzodiazepine site (sometimes referred to as the benzodiazepine or BDZ receptor), the GABAA receptor contains sites of interaction for several other classes of drugs. These include a steroid binding site, a picrotoxin site, and a barbiturate site. The benzodiazepine site of the GABAA receptor is a distinct site on the receptor complex that does not overlap with the site of interaction for other classes of drugs that bind to the receptor or for GABA (see, e.g., Cooper, et al., The Biochemical Basis of Neuropharmacology, 6th ed., 1991, pp. 145-148, Oxford University Press, New York).
In a classic allosteric mechanism, the binding of a drug to the benzodiazepine site increases the affinity of the GABA receptor for GABA. Benzodiazepines and related drugs that enhance the ability of GABA to open GABAA receptor channels are known as agonists or partial agonists depending on the level of GABA enhancement. Other classes of drugs, such as xcex2-carboline derivatives, that occupy the same site and negatively modulate the action of GABA are called inverse agonists. A third class of compounds exists. These compounds occupy the same site as both the agonists and inverse agonists and yet have little or no effect on GABA activity. These compounds will, however, block the action of agonists or inverse agonists and are thus referred to as GABAA receptor antagonists.
The important allosteric modulatory effects of drugs acting at the benzodiazepine site were recognized early, and the distribution of activities at different subtype receptors has been an area of intense pharmacological discovery. Agonists that act at the benzodiazepine site are known to exhibit anxiolytic, sedative, and hypnotic effects, while compounds that act as inverse agonists at this site elicit anxiogenic, cognition enhancing, and proconvulsant effects. While benzodiazepines have enjoyed long pharmaceutical use as anxiolytics, these compounds are known to exhibit a number of unwanted side effects. These include cognitive impairment, sedation, ataxia, potentiation of ethanol effects, and a tendency for tolerance and drug dependence.
GABAA selective ligands also act to potentiate the effects of certain other CNS active compounds. For example, there is evidence that selective serotonin reuptake inhibitors (SSRIs) display greater antidepressant activity when used in combination with GABAA selective ligands than when used alone.
This invention provides oxo-imidazopyridine-carboxamide derivatives that bind with high affinity and high selectivity to the benzodiazepine site of GABAA receptors, including human GABAA receptors. Compounds of the invention bind, preferably with high selectivity and affinity, to GABAA receptors and thereby act as agonists, antagonists or inverse agonists of such receptors. As such, they are useful in the treatment of various CNS disorders.
The compounds of the invention bind with high selectivity and high affinity to the benzodiazepine site of GABAA receptors.
The invention provides compounds of Formula I (shown below), and pharmaceutical compositions comprising compounds of Formula I.
The invention further comprises methods of treating patients suffering from certain CNS disorders with an effective amount of a compound of the invention. The patient may be a human or other mammal. Treatment of humans, domesticated companion animals (pets) or livestock animals suffering from certain CNS disorders with an effective amount of a compound of the invention is encompassed by the invention.
In a separate aspect, the invention provides a method of potentiating the actions of other CNS active compounds. This method comprises administering an effective amount of a compound of the invention in conjunction with the administration of another CNS active compound.
In another, aspect this invention relates to the use of compounds of Formula I as probes for the localization of GABAA receptors in tissue sections. Such probes may be used in vitro (e.g., in binding assays) or in vivo (e.g., in PET or SPECT Scans).
Accordingly, in a broad aspect, the invention is directed to compounds of Formula I 
and the pharmaceutically acceptable non-toxic salts thereof wherein:
A, B and C independently represent hydrogen, halogen, C1-C6 alkyl,
wherein said C1-C6 alkyl is straight, branched or cyclic, contains zero, one or two double or triple bonds, and is unsubstituted or substituted with one or more substituents selected from hydroxy, oxo, halogen, amino, mono- or di(C1-C6)alkylamino, C1-C3 alkoxy, and C3-C7 cycloalkyl,
C1-C6 alkoxy, C1-C6 haloalkyl, hydroxy, amino, mono- or di(C1-C6)alkylamino, C3-C7 cycloalkyl, mono- or di(C1-C6)alkylamino (C1-C6) alkyl, mono- or di(C1-C6)alkylamino (C1-C6)alkoxy, aryl(C1-C6)alkyl and substituted aryl(C1-C6)alkyl;
E is selected from hydrogen, hydroxy, C1-C6alkyl, and C1-C6 mono- or di(C1-C6)alkyl amino(C1-C6)alkyl;
F is selected from hydrogen, halogen, hydroxy, amino, and C1-C6 alkyl;
G is selected from aryl and heteroaryl, each of which is optionally substituted with up to three groups independently selected from the group consisting of halogen, C1-C6 alkyl, C1-C6 alkoxy, C1-C6 haloalkyl, hydroxy, mono- or di(C1-C6)alkylamino, and C1-C6 alkyl substituted with one or two groups independently selected from xe2x80x94OR2, xe2x80x94NR6R7, and heterocycloalkyl, where R2, R6 and R7 are the same or different and represent hydrogen, C1-C6 alkyl, or C3-C7 cycloalkyl, or NR6R7 represents a cyclic moiety having 3-7 members.
In another aspect, the invention provides intermediates useful for preparing the compounds of Formula I.
In a further aspect, the invention provides methods for making compounds of Formula I.
The compounds encompassed by the invention are represented by general Formula I (set forth above). The invention includes the pharmaceutically acceptable salts of those compounds.
Preferred compounds of Formula I (hereinafter compounds of Formula IA) are those where
A, B and C are independently chosen from
(i) hydrogen, halogen, C1-C6 alkoxy, C1-C6 haloalkyl, hydroxy;
(ii) C1-C6 alkyl, C3-C7 cycloalkyl, C2-C6 alkenyl, or C2-C6 alkynyl,
where each alkyl, cycloalkyl, alkenyl, or alkynyl is optionally substituted with one or more of hydroxy, oxo, halogen, amino, C1-C6 haloalkyl, C3-C7 cycloalkyl, C1-3 alkoxy, or mono- or dialkylamino;
(iii) R3R4Nxe2x80x94 where
R3 and R4 independently represent hydrogen, C1-C6 alkyl, amino (C1-C6)alkyl, (C1-C6)alkoxy (C1-C6)alkyl, or C3-C7 cycloalkyl; or
NR3R4 represents heteroaryl or heterocycloalkyl;
E is hydrogen; or
E is C1-C6 alkyl, amino(C1-C6)alkyl, mono or di(C1-C6alkyl)amino(C1-C6)alkyl, or C1-C6alkoxy(C1-C6)alkyl, each of which alkyl portion being unsubstituted or substituted with one or more of halogen, hydroxy, C3-C7 cycloalkyl, aryl, heterocycloalkyl, or heteroaryl;
F is selected from hydrogen, halogen, hydroxy, amino, and C1-C6 alkyl; and
G is selected from:
(i) a group of the formula 
xe2x80x83where R11, R11xe2x80x2, R12, R12xe2x80x2, and R13 are the same or different and are selected from
hydrogen, halogen, C1-C6 alkyl, hydroxy, trifluoromethyl, xe2x80x94OR2, and xe2x80x94NR6R7 
where R2, R6 and R7 are the same or different and are selected from hydrogen, C1-C6 alkyl, and C3-C7 cycloalkyl; or
NR6R7 represents aryl or heterocycloalkyl;
(ii) a group of the formula: 
xe2x80x83where Y is C1-C6 alkylene, and
R11 and R11xe2x80x2 are as defined above;
(iii) a group of the formula: 
xe2x80x83where R6, R7, R11, and R11xe2x80x2 are as defined above; and
Z is C1-C6alkylene or C1-C6alkyleneoxy;
(iv) a group of the formula: 
xe2x80x83where Z, R6, R7, R11, R11xe2x80x2, and R13 are as defined above;
(v) a group of the formula: 
xe2x80x83where R11, R12, and R13 are as defined above, and R14, R15, R16, and R17 are the same or different and independently carry the same definition as R11;
(vi) a group of the formula: 
xe2x80x83where R11, R11xe2x80x2, R12, R14, R15, R16, and R17 are as defined above;
(vii) a group of the formula: 
xe2x80x83where Q represents a heteroaryl group.
In specific embodiments, Z is methylene, ethylene, methyleneoxy or ethyleneoxy.
The invention encompasses compounds of Formula III: 
where A, B, C, R11, R11xe2x80x2, and Y are as defined above for Formula IA.
Thus, the invention encompasses compounds of Formula II: 
where A, B, C, R11, R11xe2x80x2, R12, R12xe2x80x2 and R13 are as defined above for Formula IA.
The invention encompasses compounds of Formula IV: 
where A, B, C, R11, R11xe2x80x2, R12, Z, R6, and R7 are as defined above for Formula IA.
The invention encompasses compounds of Formula V: 
where A, B, C, R11, R11xe2x80x2, R13, Z, R6, and R7 are as defined above for Formula IA.
The invention encompasses compounds of Formula VI: 
where A, B, C, R11, R12, R13, R14, R15, R16, and R17 are as defined above for Formula IA.
The invention encompasses compounds of Formula VII: 
where A, B, C, R11, R12, R11xe2x80x2, R14, R15, R16, and R17 are as defined above for Formula IA.
The invention encompasses compounds of Formula VIII: 
where A, B and C are as defined above for Formula IA; and Q is heteroaryl.
The invention encompasses compounds of Formula IX: 
where A, B, C and G are as defined above for Formula IA.
The invention encompasses compounds of Formula X: 
where R3, R4, B, C, and G are as defined above for Formula IA, and X is C1-C6 alkylene.
The invention encompasses compounds of Formula XI: 
where A, C, G, R3, and R4 are as defined above for Formula IA, and X is C1-C6 alkylene.
The invention encompasses compounds of Formula XII: 
where A, B, G, R3, and R4 are as defined above for Formula IA, and X is C1-C6 alkylene.
The invention encompasses compounds of Formula XIII: 
where B, C, and G are as defined above for Formula IA, R8 is defined the same as R2, and X1 is C1-C6alkylene or C1-C6 alkyleneamino.
The invention encompasses compounds of Formula XIV: 
where A, C, and G are as defined above for Formula IA, R8 is defined the same as R2, and X1 is C1-C6alkylene or C1-C6 alkyleneamino
The invention encompasses compounds of Formula XV: 
where A, B, and G are as defined above for Formula IA, R8 is defined the same as R2, and X1 is C1-C6alkylene or C1-C6 alkylene amino.
The invention encompasses compounds of formula XVI: 
where A, B, C, and G, X2 is C1-C6alkyl.
The invention encompasses compounds of Formula XVII: 
where A, B, C, and G are as defined above for Formula IA, and R9 and R10 are defined the same as R3 and R4, and X2 is C1-C6alkylene.
The invention encompasses compounds of Formula XVIII: 
where A, B, C, and G are as defined above for Formula IA, and R8 is defined the same as R2, and X2 is C1-C6alkylene.
Specific X groups are methylene and ethylene groups. Specific X1 groups are methylene, ethylene, methyleneamino and ethyleneamino groups.
Preferred compounds of general Formula I are those where G is the group: 
Z is alkyleneoxy or alkylene; and
NR6R7 represents a 5- or 6-membered heteroaryl ring. Such preferred compounds are hereinafter referred to as compounds of Formula IB. Particularly preferred compounds of Formula IB are those where the 5- or 6-membered heteroaryl ring is imidazole, triazole, or pyrazole.
Other preferred compounds of Formula I are those of the formula: 
where
E and G are as defined above for Formula IA or for Formula IB; and
B is hydrogen or lower alkyl.
In this latter group of compounds, B is preferably hydrogen or C1-C2 alkyl, and most preferably hydrogen or methyl.
The invention further encompasses compounds of formula XIX 
where
A, B and C are as defined for Formula I or IB;
R20 represents halogen, C1-C6 alkoxy, or benzyloxy; and
R21 represents hydrogen or halogen.
Particular compounds of Formula XIX are those where A and C are hydrogen, R20 is halogen, preferably bromo, and R21 is hydrogen. Other particular compounds of Formula XIX, are those where R20 is C1-C6 alkoxy, preferably methoxy, and R21 is hydrogen, or halogen. Still other particular compounds of Formula XIX, are those where A and C are hydrogen, R20 is C1-C6 alkoxy, preferably methoxy, R21 is halogen, preferably bromo, and B is C1-C6 alkyl.
The invention also encompasses compounds of Formula XX, 
where
A, B, C, E, G and F carry the same definitions as for Formula I or IB; and R22 represents benzyloxy or C1-C6 alkoxy, preferably methoxy.
Preferred compounds of Formula XX include those where B is C1-C6 alkyl, preferably C1-C2 alkyl, A, C, F, and E are hydrogen, and R22 is C1-C6 alkyl, preferably C1-C2 alkyl, most preferably methyl.
In certain situations, compounds of Formula I may contain one or more asymmetric carbon atoms, so that the compounds can exist in different stereoisomeric forms. These compounds can be, for example, racemates or optically active forms. In these situations, the single enantiomers (optically active forms) can be obtained by asymmetric synthesis or by resolution of the racemates. Resolution of the racemates can be accomplished, for example, by conventional methods such as crystallization in the presence of a resolving agent, or chromatography, using, for example a chiral HPLC column.
Representative compounds of the present invention, which are encompassed by Formula I, include, but are not limited to the compounds set forth in Table I and their pharmaceutically acceptable acid and base addition salts. If the compound of the invention is obtained as an acid addition salt, the free base can be obtained by basifying a solution of the acid salt. Conversely, if the product is a free base, an addition salt, particularly a pharmaceutically acceptable addition salt, may be produced by dissolving the free base in a suitable organic solvent and treating the solution with an acid, in accordance with conventional procedures for preparing acid addition salts from base compounds.
Non-toxic pharmaceutical salts include salts of acids such as hydrochloric, phosphoric, hydrobromic, sulfuric, sulfinic, formic, toluenesulfonic, methanesulfonic, nitic, bencoic, citric, tartaric, maleic, hydroiodic, alkanoic such as acetic, HOOCxe2x80x94(CH2)nxe2x80x94COOH where n is 0-4, and the like. Non-toxic pharmaceutical base addition salts include salts of bases such as sodium, potassium, calcium, ammonium, and the like. Those skilled in the art will recognize a wide variety of non-toxic pharmaceutically acceptable addition salts.
The present invention also encompasses the acylated prodrugs of the compounds of Formula I. Those skilled in the are will recognize various synthetic methodologies that may be employed to prepare non-toxic pharmaceutically acceptable addition salts and acylated prodrugs of the compounds encompassed by Formula I.
By xe2x80x9clower alkylxe2x80x9d and xe2x80x9cC1-C6 alkylxe2x80x9d is meant straight or branched chain alkyl groups having the indicated number of carbon atoms when a number is indicated. Examples of such groups are methyl, ethyl, propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, pentyl, 2-pentyl, isopentyl, neopentyl, hexyl, 2-hexyl, 3-hexyl, and 3-methylpentyl.
By xe2x80x9ccycloalkylxe2x80x9d and xe2x80x9cC3-C7 cycloalkylxe2x80x9d is meant cycloalkyl groups having 3-7 atoms such as, for example cyclopropyl, cyclobutyl, cyclopenyl, cyclohexyl, and cycloheptyl.
By xe2x80x9carylxe2x80x9d is meant an aromatic carbocyclic group having a single ring (e. g., phenyl), multiple rings (e. g., biphenyl), or multiple condensed rings in which at least one is aromatic, (e.g., 1,2,3,4-tetrahydronaphthyl, naphthyl, anthryl, or phenanthryl), which is optionally mono-, di-, or trisubstituted with, e.g., halogen, lower alkyl, lower alkoxy, C1-C6 haloalkyl, hydroxy, or mono- or di-(C1-C6)alkylamino.
In the term xe2x80x9csubstituted aryl(C1-C6)alkylxe2x80x9d, it is understood that the aryl group is substituted as provided in the preceding paragraph, i.e., one, two, or three substituents selected from, e.g., halogen, lower alkyl, lower alkoxy, C1-C6 haloalkyl, hydroxy, and mono- or di-(C1-C6)alkylamino.
By xe2x80x9clower alkoxyxe2x80x9d is meant straight or branched chain alkoxy groups having 1-6 carbon atoms, such as, for example, methoxy, ethoxy, propoxy, isopropoxy, n-botoxy, sec-butoxy, tert-butoxy, pentoxy, 2-pentyl, isopentoxy, neopentoxy, hexoxy, 2-hexoxy, and 3-methylpentoxy.
By xe2x80x9chalogenxe2x80x9d is meant fluorine, bromine, chlorine, and iodine.
By xe2x80x9chaloalkylxe2x80x9d as used herein is meant C1-C6 alkyl groups where one or more hydrogen atoms is replaced by a halogen atom. Representative examples include fluoromethyl, difluoromethyl, cloromethyl, bromomethyl, 1,2-difluoroethyl, trifluoromethyl, perfluoropropyl, 2,2-dichloropropyl, etc. A preferred haloalkyl group is trifluoromethyl.
By xe2x80x9cheteroarylxe2x80x9d or xe2x80x9caromatic heterocyclexe2x80x9d is meant one or more aromatic ring systems of 5-, 6-, or 7-membered rings containing at least one and up to four hetero atoms selected from nitrogen, oxygen, or sulfur. Such heteroaryl groups include but are not limited to thienyl, furanyl, thiazolyl, imidazolyl, (is)oxazolyl, pyridyl, pyrimidinyl, (iso)quinolinyl, naphthyridinyl, benzimidazolyl, and benzoxazolyl heterocyclic groups. These heteroaryl groups may be unsubstituted or substituted in a substitutable position with one or more groups selected independently from halogen, hydroxy, C1-C6 alkyl, C1-C6 alkoxy, C1-C6 haloalkyl, and mono- or di (C1-C6)alkylamino.
Specific examples of heteroaryl groups include: 
wherein
L is nitrogen or xe2x80x94CR11;
T is xe2x80x94NR19, oxygen, or sulfur;
R11, R12, R13, R11xe2x80x2, and R12xe2x80x2 are as defined above; and
R19 is hydrogen or C1-C6alkyl.
By xe2x80x9cheterocycloalkylxe2x80x9d or xe2x80x9cheterocyclic ringxe2x80x9d is meant saturated or partially unsaturated ring structures having from 3 to about 8 ring atoms, with at least one ring atom selected from nitrogen, oxygen, and sulfur and remaining ring atoms being carbon. Heterocyclic rings may be unsubstituted or substituted with one or more groups such as halogen, hydroxy, C1-C6 haloalkyl, C1-C6 alkyl, C1-C6 alkoxy, amino, or mono or di(C1-C6)alkylamino. Examples of such rings are piperidinyl, piperazinyl, morpholinyl, pyrrolidinyl, imidazolinyl, homopiperazinyl, and homopiperidinyl.
In terms such as di(C1-C6)alkylamino, di(C1-C6) alkylamino (C1-C6) alkyl, and di(C1-C6) alkylamino (C1-C6)alkoxy, it is understood that the selection of each alkyl portion is independent of any other alkyl portion in the group. Thus, for example, di(C1-C6)alkylamino includes N-methyl-N-propylamino, N-ethyl-N-butylamino, N-methyl-N-ethylamino, etc.
The definition of Formula I as shown in the specification and as used in the claims includes possible isomers, such as tautomers and rotamers. The Formulas IIc and IId, below, illustrate this point.
For Formula I, when Exe2x95x90H: 
The following numbering system is used to identify positions on the imidazopyridole ring system of the compounds of the invention: 
Representative compounds of the invention are shown in Table I.
The compounds of the invention interact with a GABA binding site, the benzodiazepine (BDZ) receptor, as shown in the examples.
This invention provides oxo-imidazopyridine carboxamides that bind, preferably with high affinity, to the benzodiazepine site of GABAA receptors, including human GABAA receptors. Preferred compounds are those that show high selectivity for the benzodiazepine site of GABAa receptors.
The compounds of Formula I and their salts are suitable for the diagnosis and treatment of anxiety, depression, memory impairment, Alzheimer""s dementia, Down Syndrome, sleep, cognitive and seizure disorders, and overdose with benzodiazepine drugs and for enhancement of alertness, both in human and non-human animals including companion animals, e.g. domestic pets, especially dogs and cats and livestock animals, e.g., sheep, swine and cattle.
The diseases and/or disorders that can be treated using compounds and compositions according to the invention include:
Depression:
depression, atypical depression, bipolar disorder, depressed phase of bipolar disorder.
Anxiety:
general anxiety disorder (GAD), agoraphobia, panic disorder +/xe2x88x92 agoraphobia, social phobia, specific phobia, Post traumatic stress disorder, obsessive compulsive disorder (OCD), dysthymia, adjustment disorders with disturbance of mood and anxiety, separation anxiety disorder, anticipatory anxiety acute stress disorder, adjustment disorders, cyclopthymia
Sleep Disorders:
sleep disorders including primary insomnia, circadian rhythm sleep disorder, dyssomnia NOS, parasomnias, including nightmare disorder, sleep terror disorder, sleep disorders secondary to depression and/or anxiety or other mental disorders, substance induced sleep disorder
Cognition impairment:
cognition impairment, Alzheimer""s disease, Parkinson""s disease, mild cognitive impairment (MCI), age-related cognitive decline (ARCD), stroke, traumatic brain injury, AIDS associate dementia, dementia associated with depression, anxiety or psychosis
The invention also provides pharmaceutical compositions comprising compounds of the invention.
The invention further comprises methods of treating patients in need of such treatment with an amount of a compound of the invention sufficient to alter the symptoms of a CNS disorder. Compounds of the inventions that act as agonists at xcex12xcex23xcex32 and xcex13xcex23xcex32 receptor subtypes are useful in treating anxiety disorders such as panic disorder, obsessive compulsive disorder and generalized anxiety disorder; as well as stress disorders, including post-traumatic stress and acute stress disorders. Compounds of the inventions that act as agonists at xcex12xcex23xcex32 and xcex13xcex23xcex32 receptor subtypes are also useful in treating depressive or bipolar disorders and in treating sleep disorders. Compounds of the invention that act as inverse agonists at an xcex15xcex23xcex32 receptor subtype or xcex11xcex22xcex32 and xcex15xcex23xcex32 receptor subtypes are useful in treating cognitive disorders including those resulting from Down Syndrome, neurodegenerative diseases such as Alzheimer""s disease and Parkinson""s disease, and stroke related dementia. Compounds of the invention that act as agonists at a xcex11xcex22xcex32 receptor subtype are useful in treating convulsive disorders such as epilepsy. Compounds that act as antagonists at the benzodiazepine site are useful in reversing the effect of benzodiazepine overdose and in treating drug and alcohol addiction.
In a separate aspect, the invention provides a method of potentiating the actions of CNS active compounds that comprises administering an effective amount of a compound of the invention in combination with another CNS active compound. Such CNS active compounds include, but are not limited to the following: for anxiety, serotonin receptor (e.g. 5-HT1A) agonists and antagonists; for anxiety and depression, neurokinin receptor antagonists or corticotropin releasing factor receptor (CRF1) antagonists; for sleep disorders, melatonin receptor agonists; and for neurodegenerative disorders, such as Alzheimer""s dementia, nicotinic agonists, muscarinic agents, acetylcholinesterase inhibitors and dopamine receptor agonists. In a preferred embodiment, the invention provides a method of potentiating the antidepressant activity of selective serotonin reuptake inhibitors (SSRIs) by administering an effective amount of a GABA agonist compound of the invention in combination with an SSRI.
Combination administration can be carried out in a fashion analogous to that described by disclosed in Da-Rocha, et al., J. Psychopharmacology (1997) 11(3) 211-218; Smith, et al., Am. J. Psychiatry (1998) 155(10) 1339-45; or Le, et al., Alcohol and Alcoholism (1996) 31 Suppl. 127-132. Also see, the discussion of the use of the GABAA receptor ligand 3-(5-methylisoxazol-3-yl)-6-(1-methyl-1,2,3-triazol-4-yl) methyloxy-1,2,4-triazolo [3,4-a]phthalzine in combination with nicotinic agonists, muscarinic agonists, and acetylcholinesterase inhibitors, in PCT International publications Nos. WO 99/47142, WO 99/47171, and WO 99/47131, respectively. Also see in this regard PCT International publication No. WO 99/37303 for its discussion of the use of a class of GABAA receptor ligands, 1,2,4-triazolo[4,3-b]pyridazines, in combination with SSRIs.
The present invention also pertains to methods of inhibiting the binding of benzodiazepine compounds, such as Ro15-1788, to GABAA receptors which methods involve contacting a compound of the invention with cells expressing GABAA receptors, wherein the compound is present at a concentration sufficient to inhibit benzodiazepine binding to GABAA receptors in vitro. This method includes inhibiting the binding of benzodiazepine compounds to GABAA receptors in vivo, e.g., in a patient given an amount of a compound of Formula I that would be sufficient to inhibit the binding of benzodiazepine compounds to GABAA receptors in vitro. In one embodiment, such methods are useful in treating benzodiazepine drug overdose. The amount of a compound that would be sufficient to inhibit the binding of a benzodiazepine compound to the GABAA receptor may be readily determined via an GABAA receptor binding assay, such as the assay described in Example 9. The GABAA receptors used to determine in vitro binding may be obtained from a variety of sources, such as, for example, from preparations of rat cortex or from cells expressing cloned human GABAA receptors.
The present invention also pertains to methods for altering the signal-transducing activity, particulary the chloride ion conductance of GABAA receptors, said method comprising exposing cells expressing such receptors to an effective amount of a compound of the invention. This method includes altering the signal-transducing activity of GABAA receptors in vivo, e.g., in a patient given an amount of a compound of Formula I that would be sufficient to alter the signal-transducing activity of GABAA receptors in vitro. The amount of a compound that would be sufficient to alter the signal-transducing activity of GABAA receptors may be determined via a GABAA receptor signal transduction assay, such as the assay described in Example 10.
The GABAA receptor ligands provided by this invention and labeled derivatives thereof are also useful as standards and reagents in determining the ability of a potential pharmaceutical to bind to the GABAA receptor.
Labeled derivatives the GABAA receptor ligands provided by this invention are also useful as radiotracers for positron emission tomography (PET) imaging or for single photon emission computerized tomography (SPECT).
Additionally this invention relates to the use of compounds of Formula I as probes for the localization of GABAA receptors, e.g., in tissue sections.
Pharmaceutical Preparations
The compounds of general Formula I may be administered orally, topically, parenterally, by inhalation or spray or rectally in dosage unit formulations containing conventional non-toxic pharmaceutically acceptable carriers, adjuvants and vehicles. The term parenteral as used herein includes percutaneous, subcutaneous, intravascular (e.g., intravenous), intramuscular, or intrathecal injection or infusion techniques and the like. In addition, there is provided a pharmaceutical formulation comprising a compound of general Formula I and a pharmaceutically acceptable carrier. One or more compounds of general Formula II may be present in association with one or more non-toxic pharmaceutically acceptable carriers and/or diluents and/or adjuvants and if desired other active ingredients. The pharmaceutical compositions containing compounds of general Formula II may be in a form suitable for oral use, for example, as tablets, troches, lozenges, aqueous or oily suspensions, dispersible powders or granules, emulsion, hard or soft capsules, or syrups or elixirs.
Compositions intended for oral use may be prepared according to any method known to the art for the manufacture of pharmaceutical compositions and such compositions may contain one or more agents selected from the group consisting of sweetening agents, flavoring agents, coloring agents and preservative agents in order to provide pharmaceutically elegant and palatable preparations. Tablets contain the active ingredient in admixture with non-toxic pharmaceutically acceptable excipients that are suitable for the manufacture of tablets. These excipients may be for example, inert diluents, such as calcium carbonate, sodium carbonate, lactose, calcium phosphate or sodium phosphate; granulating and disintegrating agents, for example, corn starch, or alginic acid; binding agents, for example starch, gelatin or acacia, and lubricating agents, for example magnesium stearate, stearic acid or talc. The tablets may be uncoated or they may be coated by known techniques. In some cases such coatings may be prepared by known techniques so as to delay disintegration and absorption in the gastrointestinal tract and thereby provide a sustained action over a longer period. For example, a time delay material such as glyceryl monosterate or glyceryl distearate may be employed.
Formulations for oral use may also be presented as hard gelatin capsules wherein the active ingredient is mixed with an inert solid diluent, for example, calcium carbonate, calcium phosphate or kaolin, or as soft gelatin capsules wherein the active ingredient is mixed with water or an oil medium, for example peanut oil, liquid paraffin or olive oil.
Aqueous suspensions contain the active materials in admixture with excipients suitable for the manufacture of aqueous suspensions. Such excipients are suspending agents, for example sodium carboxymethylcellulose, methylcellulose, hydropropylmethylcellulose, sodium alginate, polyvinylpyrrolidone, gum tragacanth and gum acacia; dispersing or wetting agents may be a naturally-occurring phosphatide, for example, lecithin, or condensation products of an alkylene oxide with fatty acids, for example polyoxyethylene stearate, or condensation products of ethylene oxide with long chain aliphatic alcohols, for example heptadecaethyleneoxycetanol, or condensation products of ethylene oxide with partial esters derived from fatty acids and a hexitol such as polyoxyethylene sorbitol monooleate, or condensation products of ethylene oxide with partial esters derived from fatty acids and hexitol anhydrides, for example polyethylene sorbitan monooleate. The aqueous suspensions may also contain one or more preservatives, for example ethyl, or n-propyl p-hydroxybenzoate, one or more coloring agents, one or more flavoring agents, and one or more sweetening agents, such as sucrose or saccharin.
Oily suspensions may be formulated by suspending the active ingredients in a vegetable oil, for example arachis oil, olive oil, sesame oil or coconut oil, or in a mineral oil such as liquid paraffin. The oily suspensions may contain a thickening agent, for example beeswax, hard paraffin or cetyl alcohol. Sweetening agents and flavoring agents may be added to provide palatable oral preparations. These compositions may be preserved by the addition of an anti-oxidant such as ascorbic acid.
Dispersible powders and granules suitable for preparation of an aqueous suspension by the addition of water provide the active ingredient in admixture with a dispersing or wetting agent, suspending agent and one or more preservatives. Suitable dispersing or wetting agents and suspending agents are exemplified by those already mentioned above. Additional excipients, for example sweetening, flavoring and coloring agents, may also be present.
Pharmaceutical compositions of the invention may also be in the form of oil-in-water emulsions. The oily phase may be a vegetable oil or a mineral oil or mixtures of these. Suitable emulsifying agents may be naturally-occurring gums, for example gum acacia or gum tragacanth, naturally-occurring phosphatides, for example soy bean, lecithin, and esters or partial esters derived from fatty acids and hexitol, anhydrides, for example sorbitan monoleate, and condensation products of the said partial esters with ethylene oxide, for example polyoxyethylene sorbitan monoleate. The emulsions may also contain sweetening and flavoring agents.
Syrups and elixirs may be formulated with sweetening agents, for example glycerol, propylene glycol, sorbitol, glucose or sucrose. Such formulations may also contain a demulcent, a preservative and flavoring and coloring agents. The pharmaceutical compositions may be in the form of a sterile injectable aqueous or oleaginous suspension. This suspension may be formulated according to the known art using those suitable dispersing or wetting agents and suspending agents that have been mentioned above. The sterile injectable preparation may also be sterile injectable solution or suspension in a non-toxic parentally acceptable diluent or solvent, for example as a solution in 1,3-butanediol. Among the acceptable vehicles and solvents that may be employed are water, Ringer""s solution and isotonic sodium chloride solution. In addition, sterile, fixed oils are conventionally employed as a solvent or suspending medium. For this purpose any bland fixed oil may be employed including synthetic mono- or diglycerides. In addition, fatty acids such as oleic acid find use in the preparation of injectables.
The compounds of general Formula I may also be administered in the form of suppositories, e.g., for rectal administration of the drug. These compositions can be prepared by mixing the drug with a suitable non-irritating excipient which is solid at ordinary temperatures but liquid at the rectal temperature and will therefore melt in the rectum to release the drug. Such materials are cocoa butter and polyethylene glycols.
Compounds of general Formula I may be administered parenterally in a sterile medium. The drug, depending on the vehicle and concentration used, can either be suspended or dissolved in the vehicle. Advantageously, adjuvants such as local anesthetics, preservatives and buffering agents can be dissolved in the vehicle.
Dosage levels of the order of from about 0.1 mg to about 140 mg per kilogram of body weight per day are useful in the treatment of the above-indicated conditions (about 0.5 mg to about 7 g per patient per day). The amount of active ingredient that may be combined with the carrier materials to produce a single dosage form will vary depending upon the host treated and the particular mode of administration. Dosage unit forms will generally contain between from about 1 mg to about 500 mg of an active ingredient.
Frequency of dosage may also vary depending on the compound used and the particular disease treated. However, for treatment of most disorders, a dosage regimen of 4 times daily or less is preferred. For the treatment of anxiety, depression, or cognitive impairment a dosage regimen of 1 or 2 times daily is particularly preferred. For the treatment of sleep disorders a single dose that rapidly reaches effective concentrations is desirable.
It will be understood, however, that the specific dose level for any particular patient will depend upon a variety of factors including the activity of the specific compound employed, the age, body weight, general health, sex, diet, time of administration, route of administration, and rate of excretion, drug combination and the severity of the particular disease undergoing therapy.
For administration to non-human animals, the drug or a pharmaceutical composition containing the drug may also be added to animal feed or drinking water. It will be convenient to formulate animal feed and drinking water products with a predetermined dose of the drug so that the animal takes in an appropriate quantity of the drug along with its diet. It will also be convenient to add a premix containing the drug to the feed or drinking water approximately immediately prior to consumption by the animal.
Preferred compounds of the invention have various pharmacological properties. Such properties include, but are not limited to oral bioavailability, low toxicity, low serum protein binding and desirable in vitro and in vivo half-lifes. Penetration of the blood brain barrier for compounds used to treat CNS disorders is necessary, while low brain levels of compounds used to treat peripheral disorders are often preferred.
Assays may be used to predict these pharmacological properties. Assays used to predict bioavailability include transport across human intestinal cell monolayers, including Caco-2 cell monolayers. Toxicity to cultured hepatocyctes may be used to predict compound toxicity. Penetration of the blood brain barrier of a compound in humans may be predicted from the brain levels of the compound in laboratory animals given the compound intravenously.
Serum protein binding may be predicted from albumin binding assays. Such assays are described in a review by Oravcovxc3xa1 et al. (Journal of Chromatography B (1996) volume 677, pages 1-27).
Compound half-life is inversely proportional to the frequency of dosage of a compound. In vitro half-lifes of compounds may be predicted from assays of microsomal half-life as described by Kuhnz and Gieschen (Drug Metabolism and Disposition, (1998) volume 26, pages 1120-1127).
The present invention also pertains to packaged pharmaceutical compositions for treating disorders responsive to GABAA receptor modulation, e.g., treatment of anxiety, depression, sleep disorders or cognitive impairment by GABAA receptor modulation. The packaged pharmaceutical compositions include a container holding a therapeutically effective amount of at least one GABAA receptor modulator as described herein and instructions (e.g., labeling) indicating the contained GABAA receptor ligand is to be used for treating a disorder responsive to GABAA receptor modulation in the patient.
An illustration of the preparation of compounds of the present invention is given in Scheme 1. 
In Scheme I, the substituents A, B, B and G carry the definitions set forth above for Formula II.
The disclosures in this application of all articles and references, including patents, are incorporated herein by reference.
The invention is illustrated further by the following examples, which are not to be construed as limiting the invention in scope or spirit to the specific procedures described in them. Those having skill in the art will recognize that the starting materials and reaction conditions may be varied and additional steps employed to produce compounds encompassed by the present invention, as demonstrated by the following examples. Unless otherwise stated, the starting material and reagents employed in these syntheses are of standard commercial grade. In some cases, protection of certain reactive functionalities may be necessary to achieve some of the above transformations. In general, the need for protecting groups, as well as the conditions necessary to attach and remove such groups, will be apparent to those skilled in the art of organic synthesis.
Representative examples of methods for preparing compounds of the invention are set forth below.